Method of producing ethyl benzene



July 16, 1946.

R. M. sHEPARDsoN 2,494,104

METHOD 0F PRODUCING ETHYL BENZENE XYLENES OUTLET @5A/2EME R. M.SHEPARDSON METHOD oF4 PRODUGING mma.A BENZENE Filed Dec. 1l, 1942 July16, 1946.

2 Sheets-Sheet 2 Patented July 16, 1946 METHOD OF PRODUCING ETHYL BENZENE Robert M. Shepardson, Madison, N. J., assgnor to Standard OilDevelopment Company, a corporation of Delaware Application December 11,1942, Serial No. 468,612

2 Claims. (Cl. 26o-66S) The present invention relates to improvements inthe art of processing hydrocarbon cils and, more particularly, itrelates to the production of substituted aromatics, such as ethylbenzene styrene, by dehydrogenation of cyclo parailns.

In the prior application o'f the present inventor and another, SerialNo. 429,012, filed January 3l, 1942, entitled Production of aromatics,there is described and claimed a process for producing styrene from apetroleum distillate derived from a naphthenic crude, the saiddistillate boiling within the range of about 26S-275 F., by subjectingthe latter fraction to catalytic dehydrogenation, extracting theproducts of catalytic dehydrogenation with a selective solvent,fractionating the extract to obtain substantially pure ethyl benzene,subjecting the ethyl benzene to a dehydrogenation treatment and thenrecovering substantially pure styrene from the products of this lastdehydrogenation by controlled distillation. The styrene thus obtainedfinds uses, among others, in the production of products such assynthetic resins, but is particularly suitable as one of the rawmaterials used in the production of synthetic rubber er rubbersubstitutes.

According to my present invention, which constitutes an improvement overthe invention described in the aforesaid application, I rst subject anethyl cyclohexane fraction to solvent extraction to remove xylenes andthereafter dehydrogenate the ethylcyclohexane to form ethylbenzene whichcan then be dehydrogenated to form styrene.

In the production of styrene by dehydrogenation of ethylbenzene, it isimportant that the ethylbenzene be quite pure. The presence of xylenesgreatly reduces the amount of ethylbenzene converted to styrene, forwhich reason I wish to keep the quantity of xylenes present in theethylbenzene below Although the ethylcyclohexane fraction or cut, whichboils within the range of 260275 F., boils below the xylenes, boilingpoints of the latter in the pure state being in the range of 281-291 F.,it has been found that the xylenes boil below their true boiling pointin admixture with parailins and naphthenes, as a result of whichappreciable quantities of xylenes are found in the narrowethylcyclohexane cut of 26d-275 F. boiling range. Although the xylenesdo not interfere in the dehydrogenation of ethylcyclohexane toethylbenzene, it is not practical to separate metaand para-xylenes fromethylbenzene after the latter has been produced, and I have found thatit improves the "rocess to remove the xylenes from the ethylcyclohexanebut by solvent extraction before the latter is dehydrogenated toethylbenzene.

The main object of the present invention, therefore, is to prepare acharging stock for the production of ethylbenzene from cycloparans whichis substantially free of aromatics, such as xylene.

A more specific object of my present invention is to remove by solventextraction from an ethylcyclohexane fraction the isomeric Xylenes priorto the dehydrogenation of the ethylcyclohexane to form ethylbenzene, sothat following the dehydrogenation it will not be necessary to separatethe ethylbenzene from metaand para-xylenes, this separation beingextremely difcult.

Other and further objects of my invention will appear from the followingmore detailed description and claims.

In the accompanying drawings, Figs. I and I-A, I have shown a flow planwhich illustratesV a preferred method of carrying my invention intopractical effect.

Referring in detail to the drawings, a charging oil comprising a highlynaphthenic petroleum fraction boiling within the range of from about260-275 F. is introduced into the system thru line l, and thence pumpedby pump 3 into a solvent extraction Zone 5 where it is contacted with asolvent which has a selective solvent power for aromatics. the saidsolvent being discharged into the top .of extraction tower 5 thru lineI0. Within the tower an extract phase and a raffinate phase are formed.In the specific example I am illustrating, the solvent extraction is aliquidliquid phase, that is to say,.both the solvent which may be, forexample, SO2, and the oil are in liquid phase. Better results may beobtained by heating the oil to vaporize the same and contacting thevapors with a high boiling solvent,

' such as phenol, furfural and resorcinol. However,

these details of solvent extracting a naphthene and/ or parafnic mixturecontaining naphthenes, paraiins, and aromatics are well known to theindustry and numerous solvents suitable for this purpose are disclosedin the prior art. Later on in the present description I have given afull description of methods of solvent extracting aromatics fromnon-benzenoid hydrocarbons, and the methods later described in detail orsimilar methods may be used in the operation taking place.

A railinate phase containing the naphthenes and paranins of the chargingoil is Withdrawn through line I2, while an extract phase is withdrawnthrough line I4. The extract phase, as stated, will contain the variousisomers of xylene, and to recover and separate these and other aromaticsfrom the solvent they are discharged into a stripping tower I6 wherethey are stripped with indirect steam or by other means. The xylenes arewithdrawn from the stripper thru line 2|, are cooled in 22, thencedischarged thru line 24 into a receiving drum 3U. 'I'he disposition ofthe xylenes does not form per se the real gist of this presentinvention, but in passing, it may be said that these Xylenes may bereacted with benzene in the presence of aluminum chloride to cause aformation of toluene by interaction between benzene molecules and thexylene molecules resulting in the transfer of a methyl group from thexylene molecule to the benzene molecule. The solvent freed of itsaromatics and other hydro-carbon content may be withdrawn through line25, passed through a cooler and recycled to line IG for further use inthe process, extracting further quantities of aromatics from thecharging oil. The separated xylenes are withdrawn through line 32.

Referring back to thesolvent extraction zone, the rafnite phasewithdrawn through line I2 is discharged into a stripping zone 59 whereit is treated with indirect steam discharged into said zone through line52 in order to strip and remove solvent from the hydrocarbons. Thesolvent is withdrawn through line 64 and recycled via cooler St and line"It to line Il leading to the solvent extraction Zone 5. Thehydrocarbons are recovered from stripping tower 50 through line 60 andthence .discharged into a red coil 65 where they are heated to atemperature of 60G-1190" F., depending upon the catalyst employed,thence withdrawn through line 6l and discharged into a reactor I0containing catalyst C. The catalyst may be a IV,

V, VI, or VII group metal, metal sulfide or oxr ide, or mixtures of twoor more, such as nickel sulfide and tungsten sulfide, and the catalystitself may have the physical form of pills, pellets, extruded shapes,granules, lumps, and the like. The catalyst may be deposited on asuitable support such as activated alumina, magnesia, carbon. or evensilica, or may be of the unsupported type. Catalysts which have beenfound satisfactory are chromium sesquioxide supported on activatedalumina, the amount of the chromium oxide being 540% by weight, thebalance being theY alumina, molybdenumoxide, say -l2% by weightsupported on activated alumina, platinum, say 5% by weight, on activatedcarbon or a mixture of nickel sulde and tungsten suliide without asupport.

It is preferable in my process to discharge hydrogen into line 60 fromline 80 where it mixes with the hydrocarbons and passes with themthrough furnace @5 and then into the reaction zone, the amount ofhydrogen being from 200G-8000 cu. ft. per barrel of cold oil fed. Withhydrogen recirculation, the reactor will be maintained undersuperatmospheric pressure of 100-l000#, whereas without hydrogenrecirculation, substantially atmospheric `operation is preferable. Thefeed rate of the hydrocarbon to the reaction zone is from 0.1-10 volumesof hydrocarbon per volume of catalyst per hour on a cold oil basis. Thetemperature prevailing within the reaction Zone will vary from 600 to1000 F., depending upon the catalyst employed. With the platinumcatalyst or a mixture of nickel sulfide and tungsten suliide, lowtemperatures of 60G-900 F. are preferred whereas temperatures of90o-1000" F. are generally needed with chromium oxide or molybdenumoxide on alumina. Also, in the case of the former two catalysts, it ispreferable to add heat to the reactor while dehydrogenation is inprogress to maintain a constant temperature, this being accomplished byring small diameter, say 1 to 6 inch, tubes or maintaining these tubesin ay high temperature salt bath, these small tubes containing thecatalyst. With the latter two catalysts, however, a constant temperatureis not required through the reaction zone, and the heat of reaction canbe supplied as sensible heat in the charge stock, temperature decreasingthrough the reaction zone in this case. In the low temperature operationwith catalysts consisting of platinum on charcoal or nickel sulde plustungsten sulfide, regeneration of the catalyst by burning with air isnot required, but this will be required frequently, say after 2-24 hoursof operation, when the higher temperatures above 900 F. are employed.Under the conditions stated, the ethylcyclohexane undergoesdehydrogenation to form ethylbenzene.

The reaction products are withdrawn from reactor 'Iil through line I I8and are discharged into a separation drum IZB where gaseous and liquidproducts may be separated. The gaseous products which will containsubstantial quantities of free hydrogen and small quantities of lowmolecular weight hydrocarbons, such as methane, ethane and propane, areremoved from separating means I2@ through line I2 I and recycled bymeans of booster compressor 8I in line 80 to line E!) to provide thehydrogen-containing gas required in the reaction chamber. Part of thehydrogen-containing gas is withdrawn through the hydrogen outletindicated on the drawing. The reaction is preferably conducted underconditions such that there is no overall net consumption of freehydrogen.

The liquid product is removed from separating means 20 through line |22.This liquid product will contain substantial amounts of ethylbenzenetogether with non-aromatic hydrocarbons and possibly smaller amounts ofother aromatics. All of the dimethylcyclohexanes except cis 1,2dimethylcyclohexane which would dehydrogenate to orthoxylene have beenexcluded from the ethylcyclohexane fraction charged to dehydrogenationby choosing a fraction with a boiling range of 26o-275 F. The boilingpoints of the various dimethylcyclohexanes, ethylcyclohexane and thecorresponding aromatics are tabulated below:

Analyses obtained on the ethylcyclohexane fractions of 260-275 F.boiling range from naphthenic crudes generally do not show the presenceof appreciable quantitiesof cis 1,2 dimethylcyclohexane in which casethe dehydrogenated product would not contain appreciable ortho-xylene.However, in some cases the cis 1,2 dimethylcyclohexane has been found inwhich case ortho-xylene would be found in the dehydrogenated product. Inaddition, if the dehydrogenation reaction is carried out at temperaturesabove 900 F., some thermal decomposition and Vpolymerization generallyoccurs with the result that benzene, toluene, and a very small quantityof aromatics boiling above xylenes are produced.

If the liquid-liquid extraction method is to be employed, the liquidproducts removed from separating means |20 thru line |22 are firstintroduced into` the upper portion of a conventional solvent extractiontower |21, as shown in Fig. |-A, adapted for countercurrent iiow ofliquids. A modification of my invention involves fractionating theproduct from line |22 to recover a 250 to 300 F. fraction and sendingthis only to the solvent treater |21.

Prior to being introduced into extraction tower |21, the liquid productsare mixed with several volumes of a solvent supplied thru line |20 whichis capable of making a separation between aromatics and non-aromatics.Many different solvents of this type are known. Thus, liquid sulfurdioxide used at low temperatures, say below F., during the extraction ischosen as illustrative herein. The mixture of liquid sulfur dioxide andthe liquid products of dehydrogenation are caused to flow in tower |21countercurrent to a nonaromatic hydrocarbon diluent which is introducedinto the bottom of tower |21 thru a line |29. This non-aromatichydrocarbon diluent should have a boiling range substantially differentfrom that of liquid sulfur dioxide and the hydrocarbons in the liquidproducts. Examples of a `lower boiling diluent are pentane andisopentane. Examples of a higher boiling diluent are a paraffinic heavynaphtha and a light kerosene.

The primary function of the non-aromatic hydrocarbon diluent is what maybe called dilution displacement. rIVhis may be explained as follows:

Although parailns and naphthenes are practically insoluble in liquid SO2at temperatures below 0 F., a mixture of liquid SO2 and aromatics willdissolve an appreciable quantity of non-aromatic hydrocarbons, the totalhydrocarbon present in the extract being composed of possibly ofnon-aromatic and 80% of aromatic hydrocarbons. Some of thesenon-aromatic hydrocarbons will boil in the same range as theethylbenzene and therefore cannot be separated therefrom byfractionation. By countercurrently washing the mixture of liquid sulfurdioxide and hydrocarbons with a relatively large amount of anon-aromatic hydrocarbon having a boiling range widely different fromthe ethylbenzene, the non-aromatic hydrocarbons originally associatedwith the ethylbenzene are displaced by the non-aromatic washing agent ofwidely different boiling range. Having essentially replaced thenon-aromatic hydrocarbons originally associated with the mixture whichboils in the same range as the ethylbenzene with non-aromatics having amuch different boiling range, it is then possible to separate thenonaromatics from the ethylbenzene by fractionation.

The volume of non-aromatic hydrocarbon diluent with which the mixture ofliquid sulfur dioxide and dehydrogenated hydrocarbons is washed shouldbe at least suflicient to efect a substantial dilution displacement andmay be from 50 to 150% or more of the volume of said mixture. The volumeof non-aromatic diluent should not, however, be so great as to displacethe liquid sulfur dioxide from the mixture.

A raffinate phase which will consist chiefly of non-aromatic hydrocarbondiluent, non-aromatic hydrocarbons from the original feed and someliquid sulfur dioxide is removed from tower |21 thru line I 30. Thismixture may be distilled to recover the SO2 and the diluent (inapparatus not shown) for further use in the process. An extract phasewhich will consist chiefly of aromatic hydrocarbons, liquid sulfurdioxide and some non-aromatic hydrocarbon diluent is removed from tower|21 thru line |3| and introduced into stripping means |32 in which thesulfur dioxide is stripped out and removed thru n n d 6 line |33. Thesulfur dioxide is recycled after cooling to line |28 and reused.

'Ihe raw ethylbenzene is substantially freed of other aromatics such asthe various isomers of xylene as follows: It is withdrawn from stripper32 thru pipe |34, thence passed thru a heater |35, then passed via line|36 into a fractionating tower |31 from the bottom of which orthoxyleneis withdrawn thru line |39 while purified ethylbenzene is withdrawn thruline |40a, thence condensed in cooling coil |11 and thence conductedthru pipe |18 to ethylbenzene storage drum |19.

If the vapor-liquid extraction method is to be used, and this method isgenerally preferred, the liquid products removed from separating means|20 thru line |22 are passed directly thru valved line |40 and a heatingmeans |4| into a tower 42 adapted for countercurrent flow 'of liquid andvapor and provided with a plurality of plates |43. When this method isused, valve |3|a is closed and valve |55a, is open. Prior to theirintroduction into tower 42, the liquid products are heated in heatingmeans |4| to a temperature at which they are substantially completelyvaporized. A high boiling selective solvent which remains in liquidphase at the temperature at which the liquid products are vaporized, isintroduced into the upper portion of the tower thru a line |44. Suitableexamples of this type of selective solvent are phenol, resorcinol andfurfural. A rafnate substantially free from selective solvent is removedin vapor phase from the top of tower |42 thru line |45, is passed thru acooling and condensing means |46 and is then collected in'a tank |41. A,portion of the condensed rainate may be recycled to the top of thetower thru line |48 to act as reflux. The remainder of the raffinate isremoved from tank |41 thru line |48-a.

A liquid extract phase, which consists essentially of selective solventand aromatics, is removed from the bottom of tower |42 thru line |49 andintroduced into a stripping means |50 provided with a heating coil whichvaporizes the ethylbenzene. A portion of the extract phase may becontinuously circulated thru the bottom of tower |42 and a heating means|5| by means of pump |52. Unvaporized selective solvent is removed fromthe bottom of stripping means |50 thru line |53 and may be recycled thruline |44 to the upper portion of tower |42'. Ethylbenzene ofsubstantially pure form or at least substantially pure and free ofxylenes, except some ortho-xylene, is recovered thru line |54 anddischarged into heater |55 and thence into fractionator |31 where it isfractionated to recover pure ethylbenzene as previously explained.

The ethylbenzene fraction collected in tank |19 which may have beenobtained by either one of the two methods of solvent extractiondescribed above is removed from tank |19 thru line by means of pump |6|and forced thru line |62 into a heating means |63. The heatedethylbenzene fraction passes thence thru line |64 into a reactionchamber |65 wherein it is subjected to dehydrogenation to convert theethylbenzene to styrene. The dehydrogenation of the ethylbenzene may beeifected either by a thermal, non-catalytic reaction or by a catalyticreaction.

If the dehydrogenation of the ethylbenzene is to be a thermal reaction,chamber |65 is maintained at a temperature between 1200 and 1500 F. andunder atmospheric or subatmospheric p resrof liquid ethylbenzene pervolume of reaction space per hour in order toobtain a very short time ofContact.

If the dehydrogenation of the ethylbenzene is to be catalytic, asuitable catalyst C is placed in reaction chamber |65 and thetemperature is somewhat lower, say between 1000 and 1300 F. The feedrate may be of the order of 0.1 to 10 volumes of liquid ethylbenzene pervolume of Ycatalyst per hour depending upon the nature of the catalystused. The pressure may be atmospheric or below atmospheric and diluentssuch as steam or inert gas may be used. The other conditions may beessentially the same as in the thermal type of dehydrogenation. A goodcatalyst for use in reaction chamber |65 is that described in theapplication of Kenneth K. Kearby, Serial No. 430,873, led February 14,1942, which consists of Parts by weight MgO 50 to 95 FezOa 3 to 49 KzO0.5 to 10 CuO 0.5 t 20 with the preferred composition being:

Parts byweight MgO '72.4 FezOa 18.4 KzO 4.6 CuO 4.6

Whichever type of dehydrogenation is carried out in reaction chamber|65, the products of reaction are removed therefrom thru line |61,passed thru a coolin-g means |68 and thence into a separating means |69.cluding hydrogen, which may be recycled to reactor of thedehydrogenation are removed from separating means |69 thru line |10.Liquid products of the dehydrogenation are removed from separating means|69 thru line |1|, thence passed thru heating means |12 and introducedinto tower |13 which is the first of a series of distillation towers forthe separation of styrene from ethylbenzene and other products which maybe associated with it. From the rst tower |13 benzene and toluene aretaken overhead thru line |14. The bottoms are passed into a second tower|15 from which ethylbenzene is taken overhead thru line |16 and afterpassing thru a cooling means |11, may be returned to tank |19. Thebottoms from tower |15 are passed thru line |86 into a third tower |80from which the desired styrene is taken overhead thru line |3| and afterbeing cooled in cooling means |82, is collected in tank |83. The bottomsfrom tower |80, which will consist essentially of polymerized fractions,are removed thru line |84. The distillation in towers |13, |15 and |19is preferably conducted under vacuum or in the presence of steam inorder to permit reduced temperatures. It is also desirable to introducea small quantity of an inhibitor Gaseous products, in-Y into the upperportion of each tower to inhibit the polymerization of the styrene.

In the operation of the process, it will be understood that manyvariations may be made in the operating details without departing fromthe spirit and scope of the invention. For example, the reactions inreaction chambers 10 and |65 may be conducted in the presence of finelydivided catalysts suspended in the vapors to be treated instead of inthe presence of rigidly arranged stationary catalysts as illustrated inthe drawings. From time to time when the catalysts C and C requireregeneration to restore their activity, this may be accomplished in anysuitable manner as, for example, by shutting off the flow of hydrocarbonvapors and passing hot, inert gases containing regulated quantities ofair or oxygen thru the catalyst mass to remove the carbonaceouscontaminants by combustion. It will be understood that if the catalystis used in iinely divided, suspended form, regeneration cannot be insitu as would be the case when the catalyst is used in stationary formbut must be effected outside the reaction chambers. The method ofregeneration, however, will be essentially the same in both cases.y

I claim:

l. A process of producing ethyl benzene which comprises solventtreating, with a liquid solvent having preferential solvent power foraromatics, a petroleum oil fraction boiling in the range from 260 F. to275 F. and containing ethyl cyclohexane with xylenes but substantiallyfree from dimethyl cyclohexanes that boil below260 F. to remove thexylenes, thereafter converting' into ethyl benzene the ethyl cyclohexanein the solvent-treated fraction, freed of the xylenes, by'

dehydrogenation under superatmospheric pressure at a temperature of fromabout 600 to 1100 F. with added hydrogen in the presence of a catalystcontaining a component selected from the class consisting of metals,oxides, and sulfides of metallic elements in groups IV, V, VI, and VIIIof the periodic system, and recovering the ethyl benzene product.

2. A process of producing ethyl benzene which comprises solventtreating, with a liquid solvent having a preferential solvent power foraromatics, a petroleum oil fraction boiling in the range from 260 F. to275 F., and containing ethyl cyclohexane with xylenes but substantiallyfree from dimethyl cyclohexanes that boil below 260 F. to remove thexylenes, thereafter converting into ethyl benzene the ethyl cyclohexanein the solvent-treated fraction, freed of the xylenes, bydehydrogenating the ethyl cyclohexane in said solvent-treated fractionunder superatmosphericpressure of to 1000 pounds persquare inch at. atemperature of from about 600 F. to 1100 F.

with added hydrogen in an amount of 2000 to 8000 cubic feet per barrelof the solvent-treated fraction on a cold feed basis in the presence ofacatalyst containing a component selected from the class consisting ofmetals, oxides, and suldes of metallic elements in groups IV, V, VI, andVIII of the periodic system, the feed rate of the solventtreatedfraction into contact with the catalyst being 0.1 to 10 volumes of oilper volume of catalyst per hour on a cold oil basis, and recovering theethyl benzene product formed in the dehydrogenation.

ROBERT M. SHEPARDSON.

